Health Risks from Exposure to Low Levels of Ionizing Radiation BEIR VII Phase 2 (2006) / Chapter Skim
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Public Summary & Executive Summary
Public Summary & Executive Summary
Pages 1-18
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· evidence for adverse health effects such as cancer and Despite these challenges, a great deal about this topic is hereditary disease, well understood. Specifically, substantial evidence exists · the BEIR VII risk models, that exposure to high levels of ionizing radiation can cause · what bodies of research the committee reviewed, illness or death.
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The early indications of health effects after high radiation exposures are too many to chronicle in this Public Summary, but the committee notes one frequently cited example. In WHAT IS MEANT BY LOW DOSES OF IONIZING 1896, Thomas Edison developed a fluoroscope that consisted RADIATION of a tapered box with a calcium tungstate screen and a view- For this report, the committee has defined low dose as ing port by which physicians could view X-ray images.
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population exposure, while manpercentage of natural ionizing radiation exposure comes made sources contributed 18% (see Figure PS-2, pie chart in from cosmic rays, followed by terrestrial sources, and "in the lower left portion of the figure)
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. Because this report evaluates the health effects of low-LET radiation, the low-LET portion of the pie chart is separated to illustrate the relative contributions of the three major sources of low-LET radiation exposure.
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Food and Drug perience diagnostic radiation exposure related to cardiac Administration web site.13 catheterization and of premature infants who are monitored with repeated X-rays for pulmonary development. CT Scans Used in Diagnostic Procedures Working near Ionizing Radiation The use of CT scans in adults experiencing symptoms of illness or injury is widely accepted, and CT scan use has People who work at medical facilities, in mining or millincreased substantially in the last several decades.
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It then gives an example derived from the lations such as those of Hiroshima and Nagasaki. BEIR VII risk models using a figure with closed circles rep As noted above, the most thoroughly studied individuals resenting the frequency of cancers in the general population for determination of the health effects of ionizing radiation and a star representing estimated cancer incidence from raare the survivors of the Hiroshima and Nagasaki atomic bombs.
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Source: Modified from Brenner and colleagues.17 diation exposure using the BEIR VII risk models. Next, the section explains how the absence of evidence for induced adverse heritable effects in the children of survivors of atomic bombs is consistent with the genetic risk estimated through the use of the doubling dose method in this report.
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The initial goal of the mouse experiments was to examine the effects of different doses, types, and modes of delivery of radiation on mutation frequencies and the extent to which Health Effects Other Than Cancer the germ cell stages in the two sexes might differ in their In addition to cancer, radiation exposure has been dem- responses to radiation-induced mutations. As it turned out, onstrated to increase the risk of other diseases, particularly however, the continuing scarcity of data on radiation-incardiovascular disease, in persons exposed to high therapeu- duced mutations in humans and the compelling need for tic doses and also in A-bomb survivors exposed to more quantitative estimates of genetic risk to formulate adequate modest doses.
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The BEIR VII comnisms underlying naturally occurring genetic diseases and mittee has concluded that radiation health effects research, radiation-induced mutations in experimental organisms in- taken as a whole, does not support this view. In essence, the cluding the mouse.
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The main studies establishing the health rence of radiation-induced cancers at low doses will be small. effects of ionizing radiation are those analyzing survivors of The committee maintains that other health effects (such as the Hiroshima and Nagasaki atomic bombings in 1945.
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In this report, the committee has data suggest enhancement or reduction in radiation effects defined low doses as those in the range of near 0 up to about and in some cases appear to be restricted to special experi100 milligray (mGy) of low-LET radiation, with emphasis mental circumstances.
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In particular, evidence has been obtained that major doses of low-LET irradiation, the genetic risks are very small deficiencies in DNA damage response and tumor-suppres- compared to the baseline frequencies of genetic diseases in sor-type genes can serve to elevate radiation cancer risk. the population.
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However, noncancer risks at the low doses of interest on the effects of age at exposure or of exposure protraction. for this report are especially uncertain, and the committee For stomach cancer, the estimates of ERR per gray range has not modeled the dose-response for nonneoplastic dis- from negative to 1.3.
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The application of a new approach to genetic risk estimation leads Environmental Studies the committee to conclude that low-dose induced genetic risks are very small when compared to baseline risks in the Ecological studies of populations living around nuclear population. facilities and of other environmentally exposed populations · The committee judges that the balance of evidence from do not contain individual estimates of radiation dose or epidemiologic, animal, and mechanistic studies tends to faprovide a direct quantitative estimate of risk in relation to vor a simple proportionate relationship at low doses between dose.
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New data and analyses have dose ionizing radiation reduced sampling uncertainty, but uncertainties related to Currently identified molecular markers of DNA damage estimating risk for exposure at low doses and dose rates and and other biomarkers that can be identified in the future to transporting risks from Japanese A-bomb survivors to the should be used to quantify low levels of DNA damage and to U.S. population remain large.
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The insert shows the fit of a linear-quadratic model for leukemia to illustrate the greater degree of curvature observed for that cancer. Research Need 2: Determination of DNA repair fidelity, Research Need 3: Evaluation of the relevance of adapespecially with regard to double and multiple strand tation, low-dose hypersensitivity, bystander effect, breaks at low doses, and whether repair capacity is inde- hormesis, and genomic instability for radiation carpendent of dose cinogenesis Repair capacity at low levels of damage should be inves- Mechanistic data are needed to establish the relevance of tigated, especially in light of conflicting evidence for stimu- these processes to low-dose radiation exposure (i.e., lation of repair at low doses.
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including CT, positron emission tomography, and single photon emission computed tomography. Research Need 6: Genetic factors in radiation cancer risk Further work is needed in humans and mice on gene mu Research Need 9: Future occupational radiation studies tations and functional polymorphisms that influence radia Studies of occupational radiation exposures, in particular tion response and cancer risk.
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It is Research Need 12: Epidemiologic studies in general important that follow-up for mortality and cancer incidence Data from the LSS cohort of A-bomb survivors should be continue for the 45% of the cohort who remained alive at the supplemented with data on populations exposed to low doses end of 2000. and/or dose rates, especially those with large enough doses In the near future, an uncertainty evaluation of the DS02 to allow risks to be estimated with reasonable precision.
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